For comparison in quantitative terms, the evaluation of the four assessment indices (Equations (15)–(18)) was carried out (Table 11). The reduction of the runoff volume detected after the GR conversion of the existing traditional roofs ranges from a maximum value of 49.7%, for the scenario with a conversion of 100%, to a minimum value of 16.8% for the scenario with a retrofit of 5%. In general, ΔR_V is higher for the scenarios with a higher green requalification than for the ones with a lower implementation of green technologies; indeed, the average runoff reduction reaches average values across all rainfall events of about 41, 27, and 22%, respectively, for 100, 30, and 5% GR retrofit scenarios. The 1995-scenario, where the percentage of imperviousness is nearly half the 2016-scenario (10.53 against 18.42%), is the best performing scenario with an average runoff mitigation of about 47%. The 100%-scenario can only partially achieve this behavior. This finding shows the negative impact of sealing within the basin in terms of runoff production, which cannot even be compensated by a complete green conversion of the existing traditional roofs. With reference to the shape of the rainfall profile of the events, the largest reduction of the runoff volume occurs for the stratiform events characterized by lower average intensity (about 19 mm/h) and longer duration (between 16 and 58 h). For these events (21.01.2014 and 31.10.2012), the average ΔR_V across all the scenarios is, also in this case, around 40% against the 29% of the convective events (20.11.2013 and 13.09.2012) characterized by higher average intensities (respectively, of 34 and 72 mm/h) and shorter duration (between 12 and 14 h). Similar considerations can be extended to the reduction of the peak flow. ΔP_F ranges between 40.8 and 0%. In detail, for the stratiform events, its average value is around 29% while for the convective ones, it approaches 13%. It is confirmed that the reduction is higher for the 1995-scenario and 100% GR retrofit scenario with average values, respectively, of 29 and 25% and values lower than 15% on average in the other cases. The reduction of the flooded sections is significant both for stratiform and convective events and reaches maximum and minimum values of 100 and of 25%, respectively. Here too, on average, the best performing scenarios are the ones corresponding to the 1995 scenario and to the 100% GR conversion scenario. Finally, the increase in delay time is more evident for the events occurring on 13.09.2012 and 20.11.2013. For these events, the delay time ranges between 1 and 3 h. For the other two events, the time of peak discharge is delayed at most for 1 h.